Theater stage set control system

ABSTRACT

An arrangement for determining and controlling the location and movement of properties (props) and portions of the scenery of a stage set by pneumatic means.

United States Patent Inventor William M. Cruse 333 N. Norton Ave., Los Angeles, Calif. 90004 Appl. No. 790,263

Filed Jan. 10, 1969 Patented Jan. 26, 1971 THEATER STAGE SET CONTROL SYSTEM 12 Claims, 7 Drawing Figs.

US. Cl 254/93, 272/22; 91/447 Int. Cl B66f 3/24 Field of Search 254/1, 93,

[56] References Cited UNITED STATES PATENTS 2,421,274 5/1947 Levey 272/21X 2,5 70,624 10/1951 Wyckoff 91/383X 3,006,323 10/ l 961 Tilney 9 l/42OX 3,282,283 11/1966 Takeda 9l/3X Primary Examiner-Andrew R. Juhasz Assistant Examiner-David R. Melton Attorney-Henry M. Bissell ABSTRACT: An arrangement for determining and controlling the location and movement of properties (props) and portions of the scenery of a stage set by pneumatic means.

PATENTED JAN26 :sn

sum 1. or 2 INVENTOR WILLIAM M.CRUSE ATTORNEY PATENIEUJANZBISII 3558.102

SHEET 2 [1F 2 I|OV.A.C.

L52 5IA 5O -o c 55 56 T4508 Hi CONTROL PANEL eo LIMIT SWITCH SOLENOID 8 VALVE CONSOLE CABLE CYLINDER TO OTHER UNITS INVENTOR WILLIAM M. CRUSE ATTORNEY THEATER STAGE SET CONTROL SYSTEM BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to systems for controlling the arrangement of theater stage sets, and more particularly, to such systems for moving or locating at predetermined positions the props or other movable portions of the scenery of a stage set having movable scenery,

2. Description of the Prior Art It is often desirable in the staging of theatrical productions to be able to move various props and movable portions of the scenery, either onto or off the stage or from one position to another on the stage while the production is going on in full view of the audience and without the necessity for exposing the stagehands or device effecting the movement to the view of the audience. This is of particular importance in a live theater performance, as contrasted with the filming of a motion picture or recording of a television performance in which various scenes can be moved from one stage to another and can be rearranged during interruption of the actual filming or recording.

Various apparatus has been employed in the past to achieve the desired results, principally by the erection of a false stage, provided with a number of slots therein to control the direction of movement of the various props or pieces of scenery that are movable, with spacing underneath the false stage to accommodate the location of a cabling system which may be used to drive members that are attached through the slots to the corresponding props or portions of movable scenery. Initially these cables were directed via various pulleys, sheaves, gears and the like to manually driven, crankoperated drive portions accessible to human operators. More recently, these have been supplanted by similar arrangements which are driven by electric motors arranged to be controlled by a set manager. While the motor driven arrangement is an improvement over the manually driven system, it has presented a number of disadvantages. For example, with respect to larger pieces of movable scenery such as a balcony or a staircase which may weigh several hundred pounds by the time a number of actors are in position thereon, motors with substantial power are required to produce the desired movement of the scenery. This is particularly the case where a slightly inclined stage is employed, as may be done to enhance the effect of depth of the stage, since the motor driven mechanism must be generally capable of moving the corresponding portion of scenery in both directions, that is, both toward and away from the audience. Furthermore, an electric drive motor is not completely silent so that the sound of its operation is generally apparent to the spectators, at least those in the first few rows of the audience, thus detracting from the presentation of the production. Where such motors are employed, it is not possible to vary their speed of operation without the addition of particular speed control systems which further complicate the arrangements employed.

Where a theater production is on the road" so that its stage and scenery must from time to time be disassembled, moved to a theater in another city, and reassembled, the particular arrangements which are utilized for eflecting the movement of the props and portions of the scenery in the manner described are of considerable significance in the expense attendant upon the knockdown and setup of the stage. These operations are generally performed by skilled stagehands who work substantially continuously until the job is completed in order that there may be as little interruption as possible in the actual presentation of the show. Since the cost of this operation involves the payment of overtime wages, it is important to be able to minimize the time actually required for the knockdown and setup of the stage and scenery. Thus it is desirable to have as simple an arrangement as possible for the purposes above.

described. It will be appreciated that the motor driven arrangements described above, which necessarily incorporate the mounting of a motor and associated belting or gearing, pulleys and sheaves to set up the required cable runs for each item of props or movable scenery which is to be so controlled, results in a relatively complex system from the standpoint of installation.

It is therefore a general object of the present invention to provide an improved system for controlling the movement and location of theater props and scenery.

It is a further object of the present invention to provide such a system in a form which will simplify the task of installing and disassembling the equipment included therein.

SUMMARY OF THE INVENTION In brief, particular arrangements in accordance with the present invention employ a device known as a cable cylinder unit together with an associated mounting device to achieve the desired movement and positioning of particular elements of stage props and scenery in a pneumatic system controlled in accordance with the invention by particular valves and solenoids. While preferred embodiments of the invention will be described in the context of a pneumatic system, it will be understood that the principles of the invention are applicable as well to the systems utilizing pressurized liquid such as hydraulic systems.

The cable cylinders employed in the preferred arrangements of the invention consist essentially of a tubelike cylinder having a length corresponding to the desired movement of the associated item to be moved and containing a piston which is movable within the cylinder in either direction depending upon the side to which pneumatic pressure is applied. A cable having a suitable smooth covering of a material such as nylon is secured in a closed loop extending over pulleys at opposite ends of the cable cylinder to opposite faces of the enclosed piston. Thus, as the piston 'moves within the cylinder, the cable is also forced to move into one end of the cylinder and out the other and around the two pulleys. A prop or item of stage scenery is affixed to the cable and thus its position and movement are controlled in response to actuation of the cable cylinder. The ends of the cylinder are closed by caps which include bushings that permit the passage of the cable therethrough in a pressure-sealing relationship. The seal thus provided between the nylon-sheathed cable and the bushing through which it passes is sufficient to maintain the pressure in the cylinder substantially undiminished over a period of many hours without replacement. Such units are produced commercially by Tol-O-Matic, Inc., Minneapolis, Minnesota.

In accordance with the invention, a system for controlling the admission of pneumatic fluid to opposite ends of the cable cylinder includes a double-solenoid-controlled valve which may be operated to a selected one of 3 positions so that pneumatic fluid may be directed to one end of the cable cylinder, to the other end of the cable cylinder, or to both ends of the cable cylinder under equal pressure. An additional arrangement is provided under the control of another solenoid to close off the air passages communicating with the opposite ends of the cable cylinder so as to lock the cable cylinder with the piston at a selected fixed position as desired. In addition, metering valves are included in each of the lines connected with the cable cylinder, together with bypassing check valves, to control the flow of the pressurized pneumatic fluid through the lines. In accordance with an aspect of the invention, the pneumatic system is connected to a source of pressurized pneumatic fluid of sufiicient capacity and pressure to power the operation of all of the individual systems employed in a given stage set during a complete performance of a theatrical production without replenishment, thus assuring the complete absence of any noise from the operation of the system during the performance.

A plurality of such systems are employed, all preferably powered by a common pneumatic source, sufficient in number to provide the desired independent control of the movement and location of the various items of the props and stage scenery which are to be moved.

In accordance with a further aspect of the invention, certain cam-operated switches are arranged to be actuated by the movement of the cable about one of the pulleys of the cable cylinder drive mechanism so as to control the operation of the solenoids at preselected intervals and thus automatically limit the movement of the cable in response to the initiation of the travel thereof. Thus, the associated prop or item of stage scenery may be automatically positioned at a preselected spot simply by controlling the system to start it in motion toward that position with its motion being terminated at the desired location under the control of the limit switch.

By means of the described arrangements in accordance with the invention. the lines communicating with the various cable cylinders of the respective individual drive units may be brought out to a valve console where the metering valves are readily accessible for adjustment to determine the speed of operation of each individual cable cylinder unit. In one preferred embodiment, the electrical connections for the solenoids associated with the solenoid controlled valves are connected to an adjacent control panel which permits an operator to control the movement of any one or a number of separate cable cylinder units either independently or together while selecting the point at which movement is terminated for each of the units separately.

BRIEF DESCRIPTION OF THE DRAWINGS A better understanding of the invention may be had from a consideration of the following detailed description, taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a view representing a theater stage setting in which the invention may be employed to advantage;

FIG. 2 is a combination schematic and diagrammatic representation of one particular arrangement of a control system in accordance with the invention;

FIG. 3 is a schematic diagram showing electrical circuitry used in conjunction with the arrangement represented in FIG. 2 in the practice of the invention;

FIGS. 3 and 5 are side and end sectional views, respectively, showing details of a particular portion of one arrangement in accordance with the invention;

FIG. 6 is a plan view of a coupling arrangement between a cable cylinder unit and a limit switch employed in the circuitry of FIG. 3; and

FIG. 7 is a block diagram representing a control system in accordance with the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 represents a theater stage setting 10 in which arrangements in accordance with the invention may be employed to advantage. The setting 10 is shown including a raised, false stage 12, preferably prefabricated in sections for easy assembly and disassembly, to be mounted upon the regular stage of the theater. In one arrangement, the false stage 12 is inclined, increasing in elevation by approximately 1 inch to each foot of traversal from front to rear. The stage 12 is shown with a plurality of slots 14 which serve as guides for the various props and pieces of stage scenery which are to be moved. As represented in FIG. 1, a spiral staircase 16, a set bearing a balcony 18 and a backdrop 19 are shown as pieces of movable scenery which are guided'by their corresponding slots 14. The movable pieces of scenery such as items 16, 18, 19, are supported by wheels (not shown) in one particular arrangement which glide along the stage 12. Alternatively, the scenery units may be supported by air glides which are available commercially for supporting movable units such as pieces of furniture and the like.

In FIG. 2, a portion of the stage 12 is represented with a particular slot 14 therein in plan view. Below the stage 12 and supported therefrom adjacent slot 14 is a particular mechanism which is arranged to be anchored to a unit of movable scenery to control the movement and positioning thereof through the slot 14. Such movement is controlled by a cable cylinder mechanism 20 in the form of a cylinder 21, a

pair of pulleys 22 affixed to the ends thereof and a nylonsheathed cable 23. A piston (not shown) is positioned within the cylinder 21 for longitudinal movement therein. The cable 23 extends into both ends of the cylinder 21 through fluidtight seals and is attached to opposite sides of the piston within the cylinder 21. The cable 23 is also secured to an anchoring device 24 to effect the movement of the associated item of scenery.

Details of the anchoring device 24 are better shown in FIGS. 4 and 5 representing side and end elevations respectively corresponding to the plan view shown in FIG. 2. FIGS. 4 and 5 also show a portion ofa movable item of scenery such as 16 which is shown as being supported for relatively easy movement upon the stage 12 by a pair of wheels 26. A slightly tapered anchoring wedge 27 is inserted through an opening in the base of the movable scenery item 16 and is engaged by the anchoring device 24. Thus, as the anchoring device 24 is moved substantially horizontally under the control of the cable cylinder 21, the element 27 transmits a force to the movable scenery 16, causing it to follow the motion of the anchoring device 24. As shown in FIG. 5, the faces of the slot 14 are provided with nylon strips 28 to provide suitable lubricated guides for the element 27 which extends through the slot 14.

Returning to FIG. 2, the cable cylinder mechanisms 20 are commercially available devices which are well known to those skilled in the art. In preferred arrangements in accordance with the present invention, the cable cylinder unit 20 is actuated by a pneumatic circuit, electrically controlled and represented schematically in FIG. 2. Air lines 30 and 31 are connected respectively to opposite ends of the cylinder 21. Each of the air lines 30, 31 is controlled by a corresponding valve 32 or 33 which itself is air-actuated. Each of the lines 30, 31 includes an arrangement of a flow control valve 34 bypassed by a check valve 35. Each flow control valve 34 may be set to meter the flow of air leaving the cylinder 21 at a particular rate. However, the check valve 35 permits air going into the cylinder 21 to bypass the flow control valve 34 and to enter the cylinder 21 at full flow.

A master valve 36 is controlled by a pair of solenoids 38, 39 to control the flow of air between a pressure source 40 and the lines 30, 31, and also between the lines 30, 31 and the atmosphere. Each of the valves 32 and 33 is actuated by a pilot cap 42 or 43 to which air is supplied via a valve 44 controlled by a solenoid 415.

During operation of the arrangement in accordance with the invention as depicted in FIG. 2, the valves 32, 33, 36 and 44 are normally in the positions shown when the associated control solenoids 38, 39 and 45 are deenergized. The various passages shown within the symbols representing the respective valves in FIG. 2 indicate the flow or blockage of air therein. Thus, in the quiescent condition of valves 32, 33, the flow of air in the lines 30 and 31 is blocked, and whatever pressure is established within the cylinder 21 is maintained.

With the solenoid 36 in the quiescent condition as illustrated, air is directed therethrough to both of the lines 30, 31. When the solenoid 38 is energized, the valve 36 shifts to the right so that air is directed from the pressure source 40 to the valve 33 connected to the line 31. At the same time, air from the line 30 through the valve 32 is released to atmosphere after passing through the flow control valve 34. The reverse is true when the solenoid 39 is energized, the valve 36 moving to the left to direct air from the source 40 to the line 30 and to vent air from the line 31 to atmosphere. The valve 44 in the quiescent condition connects the source 40 with a blocked port and vents air from the pilot caps 42 and 43 to atmosphere. When the solenoid 45 is energized, the valve 44 moves to the left and directs air from the source 40 to the pilot caps 42, 43. The valves 32 and 33 block the passage of air through the respective lines 30, 31 when released and permit the passage of air to and from the lines 30, 31 when activated to the left-hand position.

In operation of the system shown in FIG. 2, solenoid 45 is energized when either solenoid 38 or solenoid 39 is energized. Thus, both valves 32 and 33 are opened whenever air from the pressure source 40 is directed to one or the other, but not both, of the lines 30 and 31 by the valve 36. For movement of the anchoring device 24 and its associated item of scenery in a direction from left to right as indicated in FIG. 2, air must be directed via the line 31 to the right-hand end of the cylinder 21. This is effected by energizing both the solenoid 45, which activates the valve 44 to direct air from the pressure source 40 to the pilot caps 42 and 43 to open the valves 32 and 33 respectively, and the solenoid 38, which causes the valve 36 to direct air from the pressure source 40 to the line 31. The valve 36 also vents air from the line 30 to atmosphere. The rate of release of the air from the line 30 to atmosphere is controlled by the flow control valve 34 connected in the line 30. Pressurized air from the source 40 directed via the line 31 enters the right-hand end of the cylinder 21 and applies the force against the piston contained therein, moving it from right to left and causing the cable 23 to move from left to right, transporting with it the anchoring device 24 and the associated scenery. Release of the valve 44 by deenergization of the solenoid 45 in turn releases the valves 32 and 33 and blocks both the lines 30 and 31, whether or not the valve 36 has been returned to its quiescent position. This immediately locks the position of the cable cylinder mechanism and the associated scenery at whatever point had been reached in their traverse, until the valves 32 and 33 are again opened.

In similar fashion, when the anchoring device 24 and its associated scenery is to be moved from right to left, solenoid 45 is energized, causing valve 44 to apply pressure from the source 40 to the pilot caps 42 and 43, thus opening the valves 32 and 33; and solenoid 39 is energized to cause the valve 36 to move to the left and apply pressure from the source 40 to the line at the left-hand end of the cylinder 21 and to relieve air from the line 31 to atmosphere. The resultant force on the left-hand end of the piston within the cylinder 21 causes it to move to the right and in turn transport the anchoring device 24 and its associated scenery to the left in the view shown. The speed of movement of the cable system is limited by the metering of the air from the right-hand end of the cylinder 21 via the line 31 through the flow control valve 34 in the line 31. As before, the traversal motion may be stopped at any time by deenergizing the solenoid 45 which releases the valve 44 to disconnect the pressure source from the pilot caps 42 and 43, thereby closing the valves 32 and 33 which lock the pressure within the cylinder 21 and prevent further movement of the piston therein. Thus, when a differential pressure is established across the piston within the cylinder 21, the movement of the anchoring device 24 in response thereto is maintained at a regular pace by virtue of the fact that the air leaving the low-pressure side of the cylinder 21 is metered through the associated flow control valve 34. When it is desired to lock the associated item of stage scenery at a particular position, the valves 32 and 33 are closed in response to the deenergization of the solenoid 45. This holds the scenery fixed in position against rolling, even though it may be mounted on an inclined stage.

FIG. 3 is a schematic diagram representing electrical circuitry which may be employed for controlling the system shown in FIG. 2. This circuit is provided primarily to control the activation of the solenoids 38, 39 and 45, but it also serves to provide a series of contacts in the control circuitry which establish fail-safe operation of the system as well as lighting indicator lights to inform the operator which of the circuits is energized at a given time. As shown in the circuit of FIG. 3, solenoids 38, 39 and 45 are connected on one side to a common tenninal which is returned to one side of the llO-volt lines through a switch 55. The solenoid 38 is connected in parallel with a relay while the solenoid 39 is connected in parallel with a relay 51. From the left-hand side of the solenoid 38, a circuit path is provided through back contacts 51A controlled by the relay 51, through a normally open switch 52 and a normally closed switch 56 to the other side of the I I0- volt line. The left-hand side of the solenoid 39 is connected in similar fashion through back contacts 50A of the relay 50, through a normally open switch 53 to the normally closed switch 56 and thence to the llO-volt line. Holding contacts 508 and 51B are connected respectively across the switches 52 and 53. Indicator lights 57 and 58 are provided to indicate when the circuits to the solenoids 39 and 38 respectively are energized. Solenoid 45 is connected to contacts 50C and 51C of the relays 50 and 51 respectively so as to be energized when either of the solenoid/relay parallel combinations is energized. The switch 55 is shown having five possible positions, one of which is carried directly to the right-hand side of the l 10-volt line, the others being connected respectively to the same line through normally closed contacts 60A, 60B, 60C and 60D respectively. These are contacts on a switch 60 which will be explained in connection with the description of FIG. 6 hereinbelow.

Energization of the solenoid 38 of FIG. 3 may be effected by momentary closure of the switch 52. This energizes the relay 50, assuming the relay 51 is not activated, which closes the holding contacts 50B to maintain the circuit energized and closes the contacts 50C to energize the solenoid 45 at the same time. Thus, as described hereinabove, the valves 32 and 33 of FIG. 2 are moved to a position to permit air to flow therethrough and the valve 36 is moved to the right-hand position so that air under pressure is directed to the right-hand end of the cylinder 21. For the position of the switch 55 as shown in FIG. 3, the system continues moving the associated movable item of stage scenery until the travel limit is reached. However, if the armature of the switch 55 is moved to any one of its other positions, the movement of the scenery under control of the system continues only until one of the contacts 60A-60D is opened. These are limit switch contacts which determine the extent of the travel of the associated item of movable scenery in accordance with the position selected by the setting of the switch 55. At any time during its traverse, the system can be stopped under the control of the operator simply by opening the switch 56.

In similar fashion, travel in the opposite direction is effected by energizing the solenoid 39 by momentarily closing the switch 53. This energizes the relay 51 as well, which closes the holding contacts 518 and closes the contacts 51C to energize the solenoid 45 as well. Back contacts 51A are open to ensure that the solenoid 38 cannot be energized at the same time. The lamp 57 is energized to indicate that movement is progressing in accordance with the energization of the solenoid 39. As indicated in FIG. 2, this causes air under pressure to be directed to the left-hand end of the cylinder 21. Operation with respect to the limit switch contacts 60A60D and control by means of the stop switch 56 are identical to those already described with respect to solenoid 38.

The contacts 60A-60D of FIG. 3 are part of a limit switch 60 which is shown in plan view in FIG. 6 as it is controlled by the operation of the cable cylinder mechanism 20. In the arrangement as depicted in FIG. 6, agear belt drive is coupled to the pulley 22 of the cable cylinder mechanism 20 for movement therewith. A first gear belt pulley 62 is pressed onto the shaft of the pulley 22 for movement therewith. This motion is transmitted to a second gear belt pulley 63 by a gear belt 64. Rotation of the pulley 63 is transmitted to a shaft 66 by conventional gearing (not shown). The shaft 66 extends into the limit switch 60 where it drives a series of cams which in turn actuate the contacts 60A-60D by means of cam followers individually associated therewith. One particular switch unit which may be utilized as the switch 60 is sold commercially by the Gemco Electric Company, Clawson, Michigan. The mechanism of the limit switch 60 can be preset in accordance with desired positions for interrupting the traverse of the item of movable scenery controlled by the's'ystem of FIG. 2.

FIG. 7 illustrates in block diagram form a combination of the arrangements of FIGS. 2, 3 and 6 in a complete control control panel 70, which may include one or a plurality of individual circuits of the type shown in FIG. 3, connected to control a solenoid and valve console 72, which may encompass one or a plurality of valve and solenoid arrangements as shown within the dashed outline of FIG. 2. The solenoid and valve console 72 is shown controlling the operation of one or a plurality of cable cylinder mechanisms 20. Each cable cylinder mechanism is connected mechanically to drive a limit switch 60 which in turn provides control of the circuitry of the control panel 70.

The utilization of systems in accordance with the invention for controlling the movement of theater props and items of scenery provides significant improvement in such operation with a reduction in complexity and cost over such systems which have been previously employed for this purpose. The actual device which effects the desired movement in positioning of the item of scenery is a compact and effective device for this purpose. lts structural configuration permits relatively simple mounting to the false stage with correspondingly simple disassembly when the theater set is to be taken down and moved to another location or stored. The pressurized air which is employed for actuating the cable cylinder mechanism is applied thereto through hose lines which are easily run between the valve console and the cable cylinder mechanism, and which can be easily disconnected and coiled during disassembly. Furthermore, the solenoid and valve console arrangement which controls the individual cable cylinder mechanisms is designed to be compatible with the electrical control panels that have been employed in connection with the electric motor drive systems that have previously been in use. As a result, systems of the present invention are easy to install and extremely effective in operation.

It is to be understood that the above-described arrangements are illustrative of the application of the principles of the invention. Numerous other arrangements may be devised by those skilled in the art without departing from the spirit and scope of the invention.

1 claim:

1. A system for controlling the movement and positioning of various movable items of theater stage scenery comprising:

a pressure-responsive device capable of driving a cable in either of two directions in response to selectively applied pressure;

means for fastening said cable to an item of movable stage scenery;

valve means for selectively admitting fluid under pressure to one end of said pressure-responsive device and to relieve pressure from the other end of said device;

valve means for selectively admitting pressure to the other end of said pressure-responsive device and relieving pressure from said one end of said pressure-responsive device; and

means for selectively controlling said valve means.

2. A system in accordance with claim 1 wherein said lastmentioned means comprises an electromagnetic solenoid and electrical circuitry for selectively energizing the solenoid.

3. A system in accordance with claim 2 further including means responsive to the movement of said cable for interrupting the solenoid energizing circuit at a preselected position of the cable.

4. A system in accordance with claim 3 wherein said lastmentioned means comprises a limit switch mechanically coupled to the cable driving device and driven thereby.

5. A system for controlling the movement and positioning of various movable items of theater stage scenery comprising:

a pressure-responsive device capable of driving a cable in either of two directions in response to selectively applied pressure;

means for fastening said cable to an item of movable stage scenery;

valve means for alternatively admitting fluid under pressure to one end of said pressure-responsive device and to relie ve pressure from the other end of said device, admitting pressure to the other end of said pressure-responsive device and relieving pressure from said one end of said pressure-responsive device, and applying fluid under pressure equally: to both ends of the pressure-responsive device; and

means for selectively controlling said valve means.

6. A system in accordance with claim 5 wherein the controlling means includes:

electromagnetic actuating means mechanically coupled to the valve means; and

electrical circuitry for selectively energizing the actuating means.

7. A system in accordance with claim 5 further including additional valve means connected respectively to opposite ends of the pressure-responsive device for selectively blocking the relief of pressure therefrom to fix the position of said device.

8. A system in accordance with claim 7 further including pressure-responsive means for actuating said additional valve means, a third valve means connected to control the application of fluid under pressure to said additional valve means, and means for selectively controlling the third valve means.

9. A system in accordance with claim 8 wherein both of said valve means controlling means comprise:

electromagnetic actuating means mechanically coupled to the respective valve means to be selectively controlled; and

electrical circuitry for energizing the electromagnetic actuating means of the respective valve means in unison.

10. A system in accordance with claim 5 further including an adjustable flow control valve in the pressure relief path to each end of said device for limiting the flow of fluid out of said device to a preselected flow rate.

11. A system in accordance with claim l0 further including a check valve connected in parallel with each flow control valve to bypass the flow control valve only for fluid flowing toward the pressure-responsive device.

12. A system in accordance with claim 5 wherein the pressurized fluid is compressed air and the pressure-responsive device comprises a pneumatic cylinder enclosing a piston attached to drive said cable under tension in two opposite directions. 

1. A system for controlling the movement and positioning of various movable items of theater stage scenery comprising: a pressure-responsive device capable of driving a cable in either of two directions in response to selectively applied pressure; means for fastening said cable to an item of movable stage scenery; valve means for selectively admitting fluid under pressure to one end of said pressure-responsive device and to relieve pressure from the other end of said device; valve means for selectively admitting pressure to the other end of said pressure-responsive device and relieving pressure from said one end of said pressure-responsive device; and means for selectively controlling said valve means.
 2. A system in accordance with claim 1 wherein said last-mentioned means comprises an electromagnetic solenoid and electrical circuitry for selectively energizing the solenoid.
 3. A system in accordance with claim 2 further including means responsive to the movement of said cable for interrupting the solenoid energizing circuit at a preselected position of the cable.
 4. A system in accordance with claim 3 wherein said last-mentioned means comprises a limit switch mechanically coupled to the cable driving device and driven thereby.
 5. A system for controlling the movement and positioning of various movable items of theater stage scenery comprising: a pressure-responsive device capable of driving a cable in either of two directions in response to selectively applied pressure; means for fastening said cable to an item of movable stage scenery; valve means for alternatively admitting fluid under pressure to one end of said pressure-responsive device and to relieve pressure from the other end of said device, admitting pressure to the other end of said pressure-responsive device and relieving pressure from said one end of said pressure-responsive device, and applying fluid under pressure equally to both ends of the pressure-responsive device; and means for selectively controlling said valve means.
 6. A system in accordance with claim 5 wherein the controlling means includes: electromagnetic actuating means mechanically coupled to the valve means; and electrical circuitry for selectively energizing the actuating means.
 7. A system in accordance with claim 5 further including additional valve means connected respectively to opposite ends of the pressure-responsive device for selectively blocking the relief of pressure therefrom to fix the position of said device.
 8. A system in accordance with claim 7 further including pressure-responsive means for actuating said additional valve means, a third valve means connected to control the application of fluid under pressure to said additional valve means, and means for selectively controlling the third valve means.
 9. A system in accordance with claim 8 wherein both of said valve means controlling means comprise: electromagnetic actuating means mechanically coupled to the respective valve means to be selectively controlled; and electrical circuitry for energizing the electromagnetic actuating means of the respective valve means in unison.
 10. A system in accordance with claim 5 further including an adjustable flow control valve in the pressure relief path to each end of said device for limiting the flow of fluid out of said device to a preselected flow rate.
 11. A system in accordance with claim 10 further including a check valve connected in parallel with each flow control valve to bypass the flow control valve only for fluid flowing toward the pressure-responsive device.
 12. A system in accordance with claim 5 wherein the pressurized fluid is compressed air and the pressure-responsive device comprises a pneumatic cylinder enclosing a piston attacheD to drive said cable under tension in two opposite directions. 